Effect of defoliation on seed yield of castor (Ricinus communis)

Field investigation was carried out during 2005-07 to determine yield loss to different levels of defoliation at different growth stages in 'DCS 9' castor (Ricinus communis L.) Treatments consisted of 4 defoliation levels (25, 50, 75, and 100%) at primary, secondary and tertiary spike initiation stages along with control. Per cent defoliation affected was not exactly at the prescribed levels, but nearer to them. Number of leaves removed at 25% defoliation ranged from 3 to 6, at 50% from 5 to 11 at 75% from 7 to 17 and from 10 to 25 at 100% at different stages of defoliation. The actual defoliation was 23-32% for 25% defoliation, 50-55% for 50%, 58-71% for 75% defoliation at different stages of defoliation. With increase in per cent defoliation, there was significant reduction in seed yield. The reduction in seed yield ranged from 10 to 20%, 20 to 23%, 24 to 36% and 26 to 55% with 25, 50, 75 and 100% defoliation, respectively. On an average, defoliation at primary stage showed 21% yield reduction and at secondary stage showed 33% yield reduction. Tertiary stage defoliation showed 26% yield reduction. Defoliation at secondary spike initiation stage was found to be the most sensitive stage which reduced total seed yield. The practical information generated during the study could be utilized in designing the pest management strategies in castor.